Rotary pump



May 6, 1969 A. w.1'. MOTTRAM ETAL 3,442,220

ROTARY PUMP Filed Aug. 6, 1968 Sheet of s l N E NTO RS ANTHONY WILLIAM TA5 M01- AM Jcuu Lmvsmz 5 TT Sco May 6, 1969 A. w. T. MOTTRAM ET AL3,442,220

ROTARY PUMP I Filed Aug. 6,- 1968 Sheet 3 of 5 INVENTORS Wlu. T

Amuouv IAM HOMAS MOTTQM J MN LANF'EAE ScoTT- Scorn A. w. 'r. MOTTRAMETAL 3,442,220

ROTARY PUMP May 6, 1969 Filed Aug. 6. 1968 2| Sheet 3 of a I N V E N TOR5 ANTHONY WILLIAM THOMAS Mm-TEAM JOHN LANFEAR Scorr- ScoTY UnitedStates Patent 9 ice US. Cl. 103-88 6 Claims ABSTRACT OF THE DISCLOSURE Arotary pump for liquids or liquids containing gas or vapour and capableof operating at a high rotational speed while pumping from a low suctionhead. The pump has an impeller having at least one cambered blade ofscrew-like configuration and having a thin leading edge offinelytapered, wedge-like form extending throughout the whole effectivespan of the blade from the root to the tip thereof and a blade inletangle of small magnitude, thereby to intentionally produce cavitation onthe suction side of the blade over the whole of the effective span. Theor each blade has a pitch which increases from the leading to thetrailing edge thereof and a blade angle which increases progressivelyfrom the small inlet angle to a larger outlet angle, thereby toterminate the cavitation in a region between the inlet and outlet endsof the impeller.

The invention is a continuation-in-part of Ser. No. 557,217, filed June13, 1966, now abandoned, and relates to a rotary pump for liquids orliquids containing gas hereinafter referred to as liquids.

For each constant speed characteristic of known rotary pumps, there is acritical suction head below which the delivery head and the efficiencywill fall very rapidly. The critical suction head increases as therotational speed of the pump impeller increases and so hitherto it' hasnot been possible to operate a pump at a high rotational speed where ithas been necessary to pump from a low suction head. In such cases, wherethe pump impeller is to be driven by a turbine, it has been necessary tointerpose a reduction gear between the turbine and the impeller or touse a large low speed turbine, thereby increasing the bulk and weight ofthe pump-turbine assembly. An object of the invention is to provide arotary pump which can pu'mp efficiently from a low suction head and bedriven at high speed, e.g., by a turbine, without the need for areduction gear.

Furthermore a high impeller speed in combination with a low suction headis a condition which results in the formation of cavities of gas orvapour at the inlet to the impeller. If these cavities should be allowedto form in a random manner, they would lead to obstruction of the flowof liquid through the impeller. A further object of the invention is toform said cavities in a controlled manner, thereby to produce as littledisturbance to' the flow of liquid as possible.

According to the invention, a rotary pump for liquids includes animpeller having at least one cambered blade thereon of screw-likeconfiguration, said blade having a leading edge extending throughout thewhole effective span of the blade from the root to the tip thereof, saidleading edge being of finely-tapered, wedge-like form having an includedangle of substantially 3 and thickness of between 0.5%v and 2% of theblade height at inlet and said blade having a blade angle, definedbetween the direction of rotation at a point on said blade and thetangent to the pressure face of said blade at said point, said blade3,442,220 Patented May 6, 1969 angle increasing from the leading to thetrailing edge of said blade from avalue of between 8 and 12 at inlet anda value at least 7 larger than the value at inlet at a positionsubstantially mid-way in the axial length of the impeller, a fluid inletangle, defined between the direction of rotation at a point on saidleading edge and the direction of fluid flow relative to said blade ofbetween 1 and 5, a hub to tip ratio at the inlet to said impeller ofbetween 0.2 and 0.3 and a mean blade diameter at outlet at least equalto that at the inlet to the impeller and the impeller having ameridional flow area at inlet of between 30% and larger than that at theoutlet thereof.

It has been found that a pump including an impeller having a bladegeometry as set out in the immediately preceding paragraph, whenoperated under conditions involving a cavitation number K of between 0and 0.0 4, where I =PS!M P;U

and where P =Static pressure in the pump inlet passage P =Vapourpressure of the liquid being pumped =Density of liquid, and

V =Velocity of liquid relative to the blade at the tip thereof at theimpeller inlet will operate under conditions of controlled cavitation.

During such operation, the following regions will be defined within thefiow passage through the impeller:

(I) an inlet region in which cavitation is developed on the suction sideof the blading of the impeller over the whole effective span of saidblading in a' direction from root to tip thereof,

(II) an intermediate region in which the cavitation is terminated, and

(III) a delivery region in which the flow passage is filled by theliquid being pumped and work is effected thereon.

By producing cavitation in region I as aforesaid, the full area of flowthrough the impeller at the inlet region thereof is reduced to a smallereffective value sufficient to enable an adequate fiow of liquid into theimpeller. In other words, the inlet area of the impeller is sufficientto accommodate the required liquid flow plus the volume occupied by thecavity produced by the or each blade. This enables pumping to take placeunder such conditions of high rotational speed and low suction head thatwould not have been possible with pumps designed to operate with littleor no cavitation.

In region II the cavity produced by the or each blade is terminated bycausing it to collapse inthe flow passage through the impeller away fromthe blade or other solid surfaces, as will be explained hereinafter,thereby reducing erosion damage.

In region III, after the cavitation has been terminated, the impellerwill run full and Work will be effected on the liquid being pumped.

The pump in accordance with this invention tends to beself-adjustingthereby to accommodate changes in' suction or deliveryhead, Within the design range of the pump, by movement of the saidintermediate region II towards one or other end of the impeller.

The blade may be formed on hub portions of various shapes. For example,the hub portion may be conical having its apex at the inlet end of theimpeller and may carry a single blade or several blades intertwinedaround it in the manner of a multi-start screw thread.

Impellers having screw-like cambered blades in accord- I ance with theinvention and pumps including said impellers are shown by way of examplein the accompanying drawings, in which:

FIGURE 1 shows a diagrammatic development of a cascade formed by twoadjacent blades of a multi-bladed impeller or by opposite flanks of thesame blade in two positions spaced apart by one revolution, in animpeller having only one blade;

FIGURE 2 is a perspective view looking from the inlet end of a firstimpeller;

FIGURE 3 is a view of the inlet end of the first impeller;

FIGURE 4 is a half axial section of the first impeller shown in a pumphousing;

FIGURE 5 is a half axial section similar to FIGURE 4 of a secondimpeller shown in a pump housing;

FIGURE 6 is a half axial section similar to FIGURES 4 and 5 of a thirdimpeller shown in a pump housing;

FIGURE 7 is a diagrammatic part-sectional perspective view of a pumpincluding an impeller of the kind shown in FIGURE-S 2, 3 and 4 andhaving an iris upstream of the pump inlet for effecting partialadmission thereto, the iris being shown in one extreme position in whichthe effective inlet to the impeller has a minimum area, and

FIGURE 8 is a view similar to FIGURE 7 in which the iris is shown in theother extreme position in which the effective inlet to the impeller hasa maximum area.

Referring to FIGURES 2, 3 and 4, the first impeller comprises a conicalhub 1 having screw-like blades 2 extending therefrom. On the impellerillustrated, there are three blades arranged in the manner of thethreads of a multi-start screw. Each blade 2 has a thin finely-tapered,wedge-like leading edge 3 having an included angle of substantially 3and a thickness within the range of 0.5% to 2% of the blade height and/or span at inlet. The edge may be a sharp knife-edge or it may berounded by a convex curve of small radius. These forms of leading edgeare to promote clean separation of the liquid from the flank of theblade at the suction side thereof to produce the region of cavitation,as will be described hereinafter with particular reference to FIGURE 1,and to present minimum cross-sectional area in the direction of flow,thereby to avoid undue interference by the cavitation with the flow ofliquid into the impeller. The leading edge plan-form of each blade maybe straight and extend radially from the axis of the impeller, or beinclined rearwardly or forwardly, or be curved. The leading edge alsohas a small blade inlet angle A defined between the direction ofrotation of any point on the leading edge and the tangent to thepressure face of the blade, of between 8 and 12, also for the purpose ofintentionally producing a region of cavitation, as will be explainedhereinafter with particular reference to FIG- URE 1. Each blade 2 has anoutlet edge 4.

In FIGURE 1, the blade inlet angle A, as defined hereinbefore, is theangle at the inlet edge 3 between the tangent to the pressure surface,i.e., the lower surface of a blade in FIGURE 1, and the direction ofmotion X of the blades, i.e. the direction of rotation of the impeller.The blade outlet angle B is the angle at the outlet edge 4 between thetangent to the working surface and the direction of motion X of theblades. The angle B is greater than the angle A by an amount such thatthe blade angle at a position substantially mid-way in the: axial lengthof the impeller is at least 7 larger than the blade inlet angle A. Alsothe fluid angle at inlet, the angle C, defined between the direction ofmotion X, i.e., the direction of rotation, and the direction of fluidflow relative to said blade is between 1 and 5.

The flow passage between two adjacent blades or blade positions, of theimpeller defines three regions during operation. The regions areindicated in FIGURE 1 with respect to one of the blades shown thereinand are as follows:

(I) the inlet region in which cavitation is developed on the suctionside (i.e. the upper surface in FIGURE 1) of the blades over the wholespan thereof, i.e., from root to tip;

(II) the intermediate region in which the cavitation is terminated, and

'(III) the delivery region in which the flow passage is filled by theliquid being pumped, as in a normal pump.

Although upright broken lines indicate the end of one region and thebeginning of the next region, it should be understood that the relativelengths of the regions may vary considerably from those shown,particularly as it is a feature that the position of the region oftermination of the cavitation shall be variable by self-adjustment inthe length of the impeller, thereby to accommodate changes in suction ordelivery head.

For full span cavitation in the inlet region I the blade leading edgemust be of finely-tapered, wedge-like form as aforesaid, the values ofangles A and C must be within the aforesaid limits and the value of thecavitation number K as defined hereinbefore, must be between 0 and 0.04and the hub to tip ratio at inlet must be between 0.2 and 0.3.

The following features are necessary for the collapse, i.e.,termination, of the cavity produced by the or each blade, within theregion II:

Area ratio The ratio of the areas at the inlet and outlet of theimpeller taken perpendicularly to the meridional flow line through theimpeller (that is the meridional flow area) must be such that the inletarea is between 30% and 50% larger than the outlet area. The latter areais as in conventional pumps, since the outlet region III of the impellerruns full of liquid.

Mean blade diameter In addition to the required area ratio, the meanblade diameter at outlet must be at least equal to that at inlet and ispreferably of the order of twice the mean diameter at inlet.

Blade angle In order to achieve the correct conditions for the collapseof the cavity, the blade angle of the or each blade should becomegreater towards the outlet such that its value at substantially mid-wayin the axial length of the impeller is at least 7 larger than that atinlet, the value at outlet therefore being at least 7 larger than thatat inlet.

The cavities produced in region I are indicated by bubbles 7 inFIGURE 1. The cavities are believed to collapse in the region II in theinter-blade spaces away from the blade or other solid surfaces due tothe combined effect of centrifugal force and free surface flow and thuserosion damage normally produced by cavitation is avoided or reduced.

As will be seen in FIGURE 4, the impeller is enclosed by a housing 5having a volute chamber 6 in which the kinetic energy at the outlet isdiffused as the liquid is delivered to a delivery pipe, not shown.

A pump having the impeller shown in FIGURES 2, 3 and 4 is suitable, forexample, as a high speed feed pump for a propellent in a rocket engine,as a fuel pump in a gas turbine engine or as a boiler feed pump.

The pump shown in FIGURE 5 has an impeller of which blades 2' are formedon a hub 1' of which the diameter increases slightly from inlet tooutlet or is substantially cylindrical. The blades 2' are similar to theblades 2 of the first example. The impeller is enclosed by a housing 5having a delivery vol-ute chamber 6'. The pump is intended to give alower head rise than the pump shown in FIGURE 4 and is suitable, forexample, for use as a boost or transfer pump in many applications.

The pump shown in FIGURE 6 has an impeller of which the blades areformed on a hub 1 in the manner of the blades of a centrifugal pump. The'blades 2" are similar to the blades 2 of the first example. Theimpeller is enclosed by a housing 5" having a delivery volute chamber6". The pump of FIGURE 6 is intended to give a higher head rise than thepump of FIGURE 4 and is suitable, for example, for the pumping ofliquefied gases, particularly hydrogen for rocket engines.

Since in the cavitation region I, the flow passage between adjacentblades is not completely filled with liquid, any of the foregoing pumpscan accept substantial quantities, e.g., of the order of 30% by volume,of vapour or gas without seriously affecting its hydraulic operation.Such vapour or gas may be separated from solution in the liquid byturbulence upstream of the pump inlet and therefore a pump in accordancewith this invention is suitable for operation under such conditions. Inliquefied gases, there may be bubbles of gas present and therefore thepump provided by this invention is suitable for pumping liquefied gases.

Where liquid is admitted over the whole span of the blading at inlet, apump provided by this invention will be passing its maximum fiow, thisbeing determined by the reduction of the efiective inlet area by thecavitation. Additionally, the elfective span of the blading at inlet maybe controlled by means for producing partial admission of fluid to theimpeller. By producing partial admission and keeping the net positivesuction pressure constant, the flow rate will be varied. Alternatively,by producing partial admission and varying the net positive suctionpressure appropriately, the flow may be maintained constant.

As a result of producing partial admission and of the self-adjustingability of the impeller, as described hereinbefore with regard to therelative axial lengths of the regions I, II and III, to accommodatechanges in suction or delivery head, the power required to drive theimpeller under conditions of controlled reduced fiow, is reduced, thusmaintaining the pump efiiciency. This aspect is of particular benefitwhere it is of importance to minimise the temperature rise of liquidpassing through the pump.

A suitable way in which partial admission can be effected is to providean iris immediately upstream of the inlet of the impeller, thereby toreduce the elfective tip diameter or to increase the effective rootdiameter of the blading at inlet. FIGURES 7 and 8 illustratediagrammatically a pump having an impeller in accordance with thisinvention and an iris controlled in accordance with the deliverypressure of the pump. In FIGURES 7 and 8, the pump comprises acylindrical housing 10, having an inlet pipe 11 and a delivery volutechamber 12 leading to a delivery pipe 13. The housing contains animpeller 14 similar to that shown in FIGURES 2 to 4 and mounted on ashaft 15. Immediately upstream of the impeller inlet there is an irisdevice 16 comprising overlapping obturating shutters 17 movable betweenthe two closed and open limiting positions shown in FIGURES 7 and 8respectively by an operating lever 18 movable in a peripheral slot 19 inthe device 16. The lever 18 is moved by a piston 20 movable in acylinder 21 by delivery pressure applied through a branch pipe 22leading from the delivery pipe 13. The delivery pressure is opposed by areturn spring 23. Instead of the piston 20, cylinder 21 and spring 23another fluid-responsive device, such as a bellows, may be employed tooperate the iris device in response to variation of pump deliverypressure.

What we claim as our invention and desire to secure by Letters Patent ofthe United States is:

1. A rotary pump for liquids or liquids containing gas including animpeller having at least one cambered blade thereon of screw-likeconfiguration, wherein the improvement comprises, said blade has aleading edge extending throughout the whole effective span of the bladefrom the root to the tip thereof, said leading edge being offinelytapered, wedge-like form having an included angle of substantially3 and thickness of between 0.5% and 2% of the blade height at inlet andsaid blade has a blade angle, defined between the direction of rotationat a point on said blade and the tangent to the pressure face of saidblade at said point, said blade angle increasing from the leading to thetrailing edge of said blade from a value of between 8 and 12 at inletand a value at least 7 larger than the value at inlet at a positionsubstantially mid-way in the axial length of the impeller, a fluid inletangle, defined between the direction of rotation at a point on saidleading edge and the direction of fluid flow relative to said blade ofbetween 1 and 5, a hub to tip ratio at the inlet to said impeller ofbetween 0.2 and 0.3 and a mean blade diameter at outlet at least equalto that at the inlet to the impeller and the impeller has a meriodionalflow area at inlet of between 30% and 50% larger than that at the outletthereof.

2. A pump as claimed in claim 1 in which the impeller has a conical hubhaving its apex at the inlet end of the impeller and having at least twoscrew-like cambered blades intertwined around the hub in the manner of amulti-start screw thread.

3. A pump as claimed in claim 1 in which said blade extendssubstantially perpendicularly to the surface of the impeller hub.

4. A pump as claimed in claim "1 having variable admission meanspositioned immediately upstream of the impeller.

5. A pump as claimed in claim 4 in which the variable admission means isan iris device operable to vary the effective area of admissionimmediately upstream of the impeller.

6. A pump as claimed in claim 5 in which said iris device iscontrollable by means responsive to the pressure of fluid delivered bythe pump.

References Cited UNITED STATES PATENTS 1,509,653 9/1924 Kaplan 103892,206,033 7/1940 'Franks 2301 14 2,726,606 12/1955 Davidison l03893,163,119 12/1964 Huppert et al. 103-89 3,168,048 2/1965 Toyokura et al103-88 3,299,821 1/ 1967 Silvern 103-88 FOREIGN PATENTS 531,831 8/1931Germany.

HENRY F. RADUAZO, Primary Examiner.

U.S. Cl. X.R. --156

